Do you trust the media? It's a weary old question, the stuff of too many earnest lectures and BBC licence fee submissions. But the latest answers (as supplied in a new book, Can You Trust the Media?, by Adrian Monck, the head of journalism at London's City University) aren't weary at all. Forget trust; it's a bust. Even raising it means you're asking the wrong question. The real problem is whether anyone - including the media - should trust you? And Gordon Brown, sitting there quietly at the back, ought to sit up and take notice too.

Once upon a distant time, Monck argues, broadcast news was in short supply. It arrived three or four times a day in 15-minute bulletins. It had scarcity value, and therefore an aura of authority. But now? The news pours 24/7 in a constant torrent via radio, TV, net and print. It is the wallpaper of modern existence, scrabbling after tiny shares of the national audience. There's no authority to that, so there has to be something different. Yes! Trust. BBC governors exit left; BBC trustees take their place. Trust us: we're pure, honest, disinterested. As opposed to those commercial chaps on the other side, who aren't.

It's a pretty thin argument, of course, especially when the first chairman of the Beeb trust winds up as chairman of ITV 10 seconds later. But what do we get for all this trusting? A relentless effort to "monetise" viewing or reading time, to put enough bums on seats to keep advertisers happy (or convince governments that the BBC is worth preserving). The underpinning of success here is consumer research, not piety - giving customers what we think they want. And the basic attitude shift that it brings in train grows profound. Authority is in charge; authority tells you what you must do, how you must behave. Trust sets up a series of corporate tests and volunteers to be measured by them. I promised ... now see if I can deliver.

That isn't exactly ubiquitous in media land. "Do editors of tabloids like the Sun or the New York Post stay awake at night worrying ... if their journalism is trusted?" Monck inquires sardonically. "Yeah, right." Put trust at the heart of this world and the process becomes inevitably self-preening, self-centred. See what a wonderful organisation we are ... and don't phone to tell us after the lines are closed.

In fact, trust is individual: it belongs to the individual viewer and reader, who measures his or her responses not according to some charter chock full of pledges, but by personal lights. We trust particular channels, papers, pundits because that's our opinion - not because Channel X tells us constantly how saintly it is. Watch, don't tell. But too much banging on about trust (attention Gordon!) gets the balances of responsibility way out of kilter - for the impact on both journalism and politics is uncannily similar.

First, it seems, you need a Vision, a kind of charter with idealistic bells and whistles. Then you need Commitment, specific pledges of delivery. And then you're tossed into the gladiatorial arena of trust where thumbs go up, or down. The emphasis rests solely on you, the deliverer. The crowd rules OK, without question. Last year, you were wonderful; this year, you're toast. But nobody dares stop to ask whether the whole game isn't a crude, deluding charade.

In the real world you know - if you're being honest - that hypocrisy comes in personalised portions. You wax disgusted about Cherie Blair's memoirs, then nip out and buy a copy. You prefer to save your 1999 Espace, not the planet. You pretend that Whitehall sets oil prices round the globe. You claim you noticed the 10p glitch in 2007, when first unveiled. You conveniently forget that you thought Mr B would be a great PM. So Crewe and Nantwich play sucked thumbs in the great arena. Yet, for all the righteous fury of the bloggers, the truth of the matter is rather more mundane.

Politicians (and media titans) make mistakes. Life is full of bad calls and wrong turnings. And pretending that there's some sort of guarantee against them is simply crass. Most of the time - from Downing Street to Fleet Street - the promises are conditioned by what researchers say the people want: not vision, but a few quid extra here or there. And there's no self-awareness of our wrath when that's not served up on cue. We shrug and bluster, "hard-working" citizens wrapped in righteous betrayal.

Should we trust the media? No: begin much further back. Begin by interrogating yourself.